Method of making laminated cores for transformers



1946' H. E. WHITE ET AL 2,393,439

METHOD OF MAKING LAMINATED CORES FOR TRANSFORMERS Fil ed May 6, 1945 INVEN TORS Her barf 5 Ma? BY WM/mwz /1. 5 /61 5&6 .ak z 3 ,06

Patented 'Jan. 22, 1946 METHOD OF MAKING LAMINATED COBES FORTRANSFORMERS Herbert E. White, Cleveland Heights, Ohio, and

, William H. Borst, Hollis, N. Y.

' Application May 6, 1943, Serial No. 485,942

8 Claims.

Our invention relates to transformers and the method of making them, andmore particularly to transformer cores and the method of making andassembling them with coils to form transformers.

Heretofore in the manufacture of transformers one practice has been toassemble a plurality of stamped laminations into a core having a closedmagnetic path, and to wind coils around portions of this closed" path tomake a transformer. This requires threading each of the numerous turnsof the coils through the center opening in the core, and does notreadily lend itself to rapid production of transformers. Another methodhas been to stamp the core laminations in variously shaped, sections,then to slip the legs through a preformed coil, and assemble thesections into substantially a continuous magnetic path. For best resultswith this .type of transformer the legs of the shaped sections should beinterlaced. This method also does not lend itself to rapid produc--tion. Many other methods have been tried but each has one or more timeconsuming operations which materially increases the cost of production.

It is an object of our invention to provide a means and method for rapidproduction of good transformers.

An object of our invention is to provide a new method for making a corefor a transformer.

Another object of our invention is to provide a new method of assemblinga core to form a trans-' former,

It is an object of our invention to provide a new method of assembling atransformer.

A further object of our invention is to provide a new and improved corefor a transformer which facilitates assembly and makes possible rapidcompletion of winding the strip a plurality of times about the mandrel.

Figure 3 shows the third step of welding together the successiveconvolutions of the magnetic material.

Figure 4 shows the wound and welded core after it has been cut into twopieces.

Figure 5 shows the core after the coils have been put in place and thetwo pieces of core connected together.

Figure 6 is a side view of Figure 5.

Figure 7 shows another form of our invention, and

Figure 8 shows still another form of our invention.

Preferred forms of our invention are shown in the drawing, although itis to be understood that other forms, which will be easily obtainedafter reading a detailed description of the invention, are considered byus as coming within the scope of our invention.

In Figure 1 we show a mandrel III which has a slot II extending alongone side thereof. Positioned in the slot is one end 9 of a long strip ofmagnetic material I! which is suitable for making transformer cores. Aconvenient material thickness for some transformers is one the order of.020 inch thick. The magnetic strip material may be oxidized, or it mayhave a layer of lacquer or other insulating material on it. After theend of I the strip I2 is placed in the slot, the material is bent andseveral complete turns of the material 12 about the mandrel are made.Tension is maintained on the strip material l2 in order to assure thatthe successive convolutions. will be tight against the previous ones.

We speak of taking turns of the strip material about the mandrel, but itis to be understood that this is only by way of example, and that on amass production basis it probably will be much quicker and moresatisfactory to mount the mandrel I 2 on a shaft I3, and to rotate theshaft. The strip material l2 can be fed from a reel (not shown) andsuitable tensioning means can be provided to assure a suitably compactcore. Due to the oxide, lacquer, or other insulating material which ison the magnetic strip l2, there will be a thin layer of insulationbetween the successive convolutions.

Figure 2 illustrates the core after the desired thickness has beenobtained by making numerous turns of the strip material I! about themandrel it. While tension is maintained on the loose end of the stripmaterial I 2, and before the mandrel is removed from the shaft II, thesuccessive convolutions are fixed together to prevent them from slippingwith respect to each other, particular care being exercised to connectthe outermost convolution to the one which is underneath it. We preferto weld across the edges of the convolutions at four places I 5, I, I1,and ID, as is shown by securing each convolution to its next adjacentconvolution, or convolutions, at four spaced points, we cut the core andthe mandrel each into two pieces along a line extending between thesewelds, thereby establishing a first cor portion 20 and a second coreportion 2|. The welds II and H are preferably adjacent the cut ends ofthe core portion 20 and prevent the convolutions from slipping withrespect to each other. The welds It and it are adjacent the cut ends ofthe core portion 2| and prevent the convolutions from slipping withrespect to each other. Each portion of the core thereby retains itsshape. It is for this reason that we apply the four welds i5, IS, IT,and |8 to the uncut core, and space them in pairs with welds i5 and I6and welds i1 and it being just far enough apart that a saw or othercutting device can pass between them.

After the core and the mandrel have been severed, each into two pieces,the mandrel can be removed from inside the core portions and 2|, and theend 9 of the strip material which was inserted into the slot H can bestraightened out or broken oil. We prefer to break it of! as it is notnecessary to the operation of our device, and this operation is fasterthan trying to straighten it. Obviously, other holding means which donot leave this bent end to be disposed of may be used. It is alsopossible to saw through the magnetic material at two places withoutcutting the mandrel III in two, thereby saving it for further use.

It is also possible to slide it sideways out of the core after the coreconvolutions have been connected together and prior to cutting themagnetic material.

Previously formed primary and secondary coils 22 and 24 comprised ofmany turns of fine wire may then be slipped onto the legs of one of thecore portions, for instance, portion 20. Insulating means l4 may beplaced between the core and the coils. We prefer to cut the core nearone of the ends as shown, thereby making one end portion 2|!substantially larger than the other end portion 2|; then the coils 23,24 are positioned on the larger end portion. After the coils have beenslipped into position the cut ends are brought together and held under aslight amount of compression, such as in a vice, and means are providedfor connecting the two end portions 20 and 2| together.

Figure 5 illustrates two such means. We prefer to weld the two portionstogether, such as is shown at points 25. It is also possible to have thewelds 25 extend the full height of the core. It is also possible to weldthe two portions together by a weld extending between welds I1 and II.It is also possible to bolt the two portions together, such as is shownat 26. A slight air gap 21 may result but this may be advantageous insome types of transformers, such as are welding transformers, and thesize of the gap may be controlled by inserting a magnetic non-conductorof desired thickness between the ends of the core portions before theyare connected together. If the two core end portions 20, 2| do not alignexactly, due to the removal of portion 9 of the magnetic material,slight pressure may be applied laterally to force them into alignment.However, due to the thinness of the strip magnetic material l2, thismis-alignment is not serious, and may be overlooked entirely.

We have shown welds IS, l6, l1, [8 only on the top surface of theconvolutions of core material because if there were a weld across thebottom edges of the convolutions as well as across the top edges therewould be established an undesirable magnetic short circuit around thelaminations.

Figure 7 illustrates another form of our invention in which the twospaced welds I! and It were replaced by a single weld ll, and the twospaced welds l1 and |l were replaced by a single weld 2|. The core wasthen cut into the two core portions 20, 2| by sawing along a line 32extending through the welds 10, 3|. In Figure 7 the two resultingportions are shown moved apart. Due to the width of the welds 2|, 8|being greater than the width of the saw cut, each cut end of each coreportion 2|, 2| will have a welded portion which will prevent theconvolutions from slipping. Either before or after cutting, the mandrelcan be removed. This method may be preferable to the previouslydescribed method as it pr bably will take less time to make one fairlywide weld than it will take to make two spaced welds.

The space between the left edge of weld ll (Fig. 3) and the right edgeof weld It, and the area of the weld 30 (Fig. 7) may be termed the weldarea" and the core should be cut in two through a weld area on each sideof the core because each of the two horseshoe-shaped core portionsremaining after the cut will then have a welded portion which keeps thelaminations of the core portion together. While it is preferable thatthe weld area" not extend over a great length of the circumference ofthe core it is possible that the welds, such as welds II, I, beseparated by considerable distance so long as the welds defining thespread apart "weld area" enclose only the straight legs of the core.Thus when the core is cut into two portions there is no tendencyoropportunity for the laminations to spread apart.

Figure 7 further illustrates how the core portion 20 is wound with acoil, in case a. pre-formed coil is not used. The core portion ismounted in two caps, 34, and II, which are designed to hold th two outends of the core portion. From each cap 34, 35 there is a bent arm I,31; the arm 21 terminating in a fixed bearing ll, and the arm I beingmounted in a bearing 40 and being connected to a motor I! which isadapted to rotate the arm 36 thereby rotating the core 2| and the armII. The arms 86, II are bent in a direction such, and are just longenough, that the axis of rotation of the system extending through thebearings 38, ill passes through substantially the center of the coreportion 2|. A reel 4| supplies wire 42 which is wound about the coreportion 20 to form a coil 43.

Figure 8 illustrates another form of invention in which the convolutionsare held together by bolts and nuts 33 instead of by welding.

The mandrel l0 about which the magnetic strip material is wound can beany shape, such as round, oval, square, oblong, etc.; and may be made ofany material. We prefer to use wood as it is inexpensive and easy to sawthrough.

Although we have described our invention with a certain degree ofparticularity, it is to be understood that it is only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of theinvention as hereinafterclaimed.

'of said convolutions to its next adjacent convolution to establish aplurality of welded areas across one edge face only of said core,cutting said core at a plurality of places each of which is between theouter ends of one of said welded areas to establish core portions,applying coil means to at least one of the core portions, and connectingthe" cut ends of said core portions together to re-form substantially aclosed mag--' netic path.

2. The method of making a transformer comprised of a core and coil meansabout said core, which comprises the steps of: spirally winding a lengthof flat magnetic material to establish a core having a plurality ofconvolutions and forming a closed magnetic path, welding said includessaid straight side portions, and then connecting said two core portionstogether to reform substantially theoriginal core.

4. The method of making a transformer comprised of a core and coil meansabout said core, which comprises the steps of providing a length of flatmagnetic core material, spirally winding said flat core material toestablish a core having a number of convolutions which define a closedmagnetic path, applying a plurality of weld means across theconvolutions on only one end face of the said core for connecting thesaid convolutions together, cutting through said core and through saidweld means thereby severing said core into at least two portions eachhaving weld means adjacent its severed ends, applying coil meanseonvolutions together in a direction across said convolutions, cuttingthrough said core and through said weld to establish two separate coreportions, the width of said weld being sufficiently greater than thewidth of the cut that each core portion includes an end portion having aportion of the weld whereby the positions of the severed convolutionswith respect to each other in each of said separate core portions ismaintained. applying coil means about at least one of said twocoreportions, and then connecting said two core portions together toreform substantially the original core.

3. The method of making a transformer comprised of score and coil meansabout said core, which comprises the steps of: spirally winding a lengthof flat magnetic material to establish a closed magnetic path cor'ehaving a plurality of eonvolutions and having two rounded portions withstraight side portions therebetween, welding said convolutions togetherin a direction across said convolutions and subaantially at one of thejunctions between a curved portion and the straight side portions,cutting through said weld to establish twosellarate dis-similar coreportions one of which includes substantially all of said straight sideportions, the width of said 7 weld being suiiiciently greater thanthewidth of said out that each of said core portions includes an endportion having a portion of the weld whereby the positions of thesevered convolutions with respect to each other in each of said separatecore portions is maintained, applyingcoilmeanstothesaidcoreportionwhichto at least one portion of said core means. vand connecting said atleast two core portions together by welding over and along the saidwelds which are adjacent the said severed ends.

5. The method as set forth in claim 1 further characterized in this:that said out ends of the core portions are connected together bywelding to reform substantially a closed magnetic path.

6'. The method as set forth in claim 2 further characterized in this:that said two core portions are connected together by welding to reformsubstantially the original core.

7. The method as set forth in claim 3 further characterized in this:that said two core portions are connected together by welding to reformsubstantially the original core.

8. In the method of making a transformer comprised of a core and coilmeans about said core. which comprises the stepsof: spirally winding alength of flat magnetic material to establish a core having a pluralityof convolutions and forming a clwed magnetic path, connecting each ofthe said convolutions to its next adjacent convolution by welding'acrosssaid convolutions at two pairs of places on one edge face only of saidcore, one pair of said welds being on one leg of said core and the otherpair of said welds being on the other leg directly across the coretherefrom, and said welds in each of said pair of welds being spacedapart a sumcient distance to just accommodate a cutting instrument be-.tween them without cutting either weld area to magnetic path.

'1 E. WHITE. WILLIAM H. BURST.

